Machines used to wrap and seal articles and packages in thermoplastic film are well known in the art. Two types of machines are commonly referred to as side-sealing and lap-sealing machines. In the typical side-sealing configuration, an article or set of articles travels, typically via a conveyer belt, toward the machine. A sheet of center-folded plastic film, having two layers, is fed from a direction, which is preferably perpendicular to the direction of the conveyer. The two layers of the film are then separated such that the article is placed between the lower layer and the upper layer. On one side of the article is the center-fold, while on the other side, there is an open edge where the two layers are not attached. The machine has several sets of belts to hold and guide the film, and a side sealing mechanism, which typically comprises a heating/sealing element that fuses or welds the two layers together and a cutting element that removes the excess material. In some embodiments, the heating element serves to cut the film as well. These elements, whether a unitary element or separate components, are referred to as the heating/sealing/cutting element throughout this disclosure. Thus, as the article passes by the side sealing mechanism, this open edge is sealed by welding the two layers together, the plastic is cut and the waste is removed and discarded. At this point, the plastic film resembles a tube, with openings at both the leading and trailing ends of the article, but sealed along both sides. As the article continues to advance, an end sealing mechanism is then employed to seal the film at the leading end of the article. The article is then advanced and the end sealing mechanism then seals the film at the trailing end of the article.
In some embodiments, the end sealing mechanism includes two heated elements which move together to simultaneously cut and seal the plastic film. In some cases, it may be desirable to allow the two heated elements to remain in contact with the film for an extended time to achieve a high quality seal. However, slowing or stopping the conveyor belt to allow this extended seal time adversely impacts throughput. Therefore, in some embodiments, the end sealing mechanism is capable of moving in the horizontal direction. This may be achieved by creating a movable carriage assembly. By moving the carriage in the upstream direction, the heated elements can be brought together earlier, and then can move together downstream with the article.
However, the motion of the movable carriage presents several challenges. First, the carriage may weigh in excess of 50 pounds, so the speed at which it moves back and forth may cause mechanical vibration in the sealing machine. Secondly, the movable carriage complicates the sealing machine, as motion in two directions, horizontal and vertical, must be synchronized.
Therefore, it would be beneficial if there were a sealing machine having a movable end seal carriage that could operate at high throughput speeds and adapt readily to different sized articles.